1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition suitably used as a chemically-amplified resist useful for microfabrication utilizing various types of radiation represented by deep ultraviolet rays such as a KrF excimer laser and ArF excimer laser, X-rays such as synchrotron radiation, and charged particle beams such as electron beams.
2. Description of Background Art
In the field of microfabrication represented by the manufacture of integrated circuit devices, lithographic technology enabling microfabrication with a line width of 0.20 xcexcm or less has been demanded in order to increase the degree of integration.
In a conventional lithographic process, near ultraviolet rays such as i-line radiation have been generally used. However, it is difficult to perform microfabrication with a line width of sub-quarter micron using near ultraviolet rays.
Therefore, in order to enable microfabrication with a line width of 0.20 xcexcm or less, utilization of radiation with a shorter wavelength has been studied. Deep ultraviolet rays represented by a bright line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given as radiation with a shorter wavelength. Of these, a KrF excimer laser (wavelength: 248 nm) and an ArF excimer laser (wavelength: 193 nm) have attracted attention.
As a resist applicable to the excimer laser radiation, a number of resists utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a component generating an acid (hereinafter referred to as xe2x80x9cphotoacid generatorxe2x80x9d) which generates an acid upon irradiation (hereinafter referred to as xe2x80x9cexposurexe2x80x9d) have been proposed. Such a resist is hereinafter called a chemically-amplified resist.
Japanese Patent Publication No. 2-27660 discloses a chemically-amplified resist containing a polymer having a t-butyl ester group of a carboxylic acid or t-butylcarbonate group of a phenol and a photoacid generator. The t-butoxycarbonyl group or t-butylcarbonate group in the polymer dissociates by the action of an acid generated upon exposure, whereby the polymer has an acidic group such as a carboxylic group or a phenolic hydroxyl group. As a result, irradiated areas of the resist film become readily soluble in an alkaline developer.
Most of the conventional chemically-amplified resists use a phenol resin as a base resin. Deep ultraviolet rays used as radiation for exposure are absorbed due to an aromatic ring in the resin and cannot sufficiently reach the lower layers of the resist film. Because of this, the dose of the radiation is greater in the upper layers and is smaller in the lower layers of the resist film. This causes a resist pattern after development to be thinner in the upper part but thicker toward the lower part, resulting in a trapezoid cross-section. No sufficient resolution can be obtained from such a resist film. If the resist pattern after development is in the shape of a trapezoid, desired dimensional accuracy cannot be achieved in a succeeding step such as an etching step or ion implantation step. Moreover, if the shape of the upper part of the resist pattern is not rectangular, the rate of removal of the resist by dry etching is increased, whereby it is difficult to control etching conditions.
The shape of the resist pattern can be improved by increasing the radiation transmittance of the resist film. For example, a (meth)acrylate resin represented by polymethylmethacrylate is a highly desirable resin from the viewpoint of radiation transmittance, because the (meth)acrylate resin has high transparency to deep ultraviolet rays. Japanese Patent Application Laid-open No. 4-226461 discloses a chemically-amplified resist using a methacrylate resin, for example. However, in spite of the excellent microfabrication performance, this composition exhibits poor dry etching resistance due to the absence of an aromatic ring, giving rise to difficulty in performing etching with high accuracy.
When a resist pattern is formed from a chemically-amplified resist composition, the composition is generally dissolved in a suitable organic solvent. The dimensional accuracy of the resist patterns, resolution, and the like are considerably affected by the type and combination of the solvent used for forming resist patterns. Moreover, when a composition solution is applied to a substrate by a spin coating method, for example, the surface of the coated resist film is not necessarily sufficiently uniform because of inadequate wettability of the composition with the substrate, giving rise to insufficient uniformity of film thickness. Furthermore, when the composition is stored as a solution, the combination of the resin and solvent affects the stability of the solution. Some compositions solution produce foreign matters during storage.
Various types of solvents such as ethers, glycol ethers, glycol ether acetates, cellosolve esters, aromatic hydrocarbons, ketones, and other esters have conventionally been used as solvents for the chemically-amplified resist composition solutions. However, it has been difficult to discover an optimal combination of the resin and solvent because of many types of solvents.
An object of the present invention is to provide a radiation-sensitive resin composition useful as a chemically-amplified resist having high transmittance of radiation and exhibiting superior basic properties as a resist such as high sensitivity and resolution and, at the same time, exhibiting excellent pattern configuration, film thickness uniformity, and storage stability.
The above object can be achieved in the present invention by a radiation-sensitive resin composition comprising:
(A) an alkali insoluble or scarcely alkali-soluble resin having an acid-dissociable protecting group of the following formula [I], 
wherein R1 groups individually represent a monovalent alicyclic hydrocarbon group having 4-20 carbon atoms or a derivative thereof, or a linear or branched alkyl group having 1-4 carbon atoms, provided that at least one of the R1 groups is the monovalent alicyclic hydrocarbon group having 4-20 carbon atoms or a derivative thereof, or any two of the R1 groups form, in combination and together with the carbon atom to which the two R1 groups bond, a divalent alicyclic hydrocarbon group having 4-20 carbon atoms or a derivative thereof, with the remaining R1 group being the linear or branched alkyl group having 1-4 carbon atoms or the monovalent alicyclic hydrocarbon group having 4-20 carbon atoms or the derivative thereof,
(B) a photoacid generator, and
(C) propylene glycol monomethyl ether acetate, xcex3-butyrolactone, and cyclohexanone as solvents.
In a preferred embodiment of the present invention, the above acid-dissociable protecting group of the-formula [I] in the resin (A) is selected from the groups of the following formulas [I-1], [I-2], and [I-3]. 
wherein the R2 group individually represents a hydrogen atom, a linear or branched alkyl group having 1-10 carbon atoms, a monovalent oxygen-containing organic group having 1-6 carbon atoms, Y1 individually represents a single bond or a group xe2x80x94CH2xe2x80x94, and n is an integer of 0-2.
The R2 group in the formulas [I-1], [I-2], and [I-3] is preferably selected from the group consisting of a methyl group, ethyl group, n-butyl group, and n-butoxy group.
The Y1 group in the formulas [I-1], [I-2], and [I-3] is preferably a single bond.
n in the formulas [I-1], [I-2], and [I-3] is preferably 0 or 1.
In another preferred embodiment, the acid-dissociable protecting group of the formula [I] in the resin (A) is included in the recurring unit of the following formula (1), 
wherein R1 is the same as defined in the formula [I] and R3 represents a hydrogen atom or a methyl group.
The amount of the recurring unit of the above formula (1) is preferably 10-60 mol % of the total recurring units in the resin (A).
In the recurring unit of the above formula (1), the group: 
is preferably dissociable in the presence of an acid and produces a carboxyl group.
The above resin (A) preferably comprises the recurring unit of the formula (1) and at least one of the recurring units of the following formulas (2-1), (2-2), (2-3), and (2-4), 
wherein R4 individually represents a hydrogen atom or a methyl group, Y2 represents a group xe2x80x94CH2xe2x80x94, xe2x80x94CH(CH3)xe2x80x94, xe2x80x94C(CH3)2xe2x80x94, xe2x80x94Oxe2x80x94, or xe2x80x94Sxe2x80x94, R5 individually represents a linear or branched alkyl group having 1-5 carbon atoms or a linear or branched alkoxyl group having 1-5 carbon atoms, j is an integer of 0 to 4, and k is an integer of 0 to 4; two or more R5 groups, present in the formula (2-3) or formula (2-4), being either the same or different, and Y2 represents a single bond or a group xe2x80x94CH2xe2x80x94.
The content of the above recurring units of the formulas (2-1), (2-2), (2-3), and (2-4) is preferably 10-80 mol % of the total recurring units in the resin (A).
In a preferred embodiment of the radiation-sensitive resin composition of the present invention, the photoacid generator (B) comprises a compound of the following formula (3), 
wherein R6 represents a hydrogen atom, hydroxyl group, linear or branched alkyl group having 1-10 carbon atoms, linear or branched alkoxyl group having 1-10 carbon atoms, or linear or branched alkoxycarbonyl group having 2-11 carbon atoms, R7 indicates a hydrogen atom or a linear or branched alkyl group having 1-10 carbon atoms, two or more R7 groups, if present, being either the same or different, p is an integer of 0-3, R8 individually represents a linear or branched alkyl group having 1-10 carbon atoms, a phenyl group or naphtyl group which may have a substituent, or two R8 groups bond, together with the sulfur atom to which the two R8 groups bond, to form a substituted or unsubstituted 3-11 member cyclic structure, m is an integer of 0-2, and Xxe2x88x92 represents a linear or branched perfluoroalkane sulfonic acid anion having 1-10 carbon atoms.
The Xxe2x88x92 group in the formula (3) is preferably at least one anion selected from the group consisting of a trifluoromethanesulfonic acid anion, nonafluoro-n-butanesulfonic acid anion, and perfluoro-n-octanesulfonic acid anion.
In another preferred embodiment of the present invention, the radiation-sensitive resin composition further comprises (D) a polycyclic compound of the formula xe2x80x94COOR9, having a molecular weight of 1,000 or less, wherein R9 represents a hydrogen atom, a linear or branched, substituted or unsubstituted alkyl group having 1-20 carbon atoms, a substituted or unsubstituted monovalent alicyclic hydrocarbon group having 3-20 carbon atoms, or a group xe2x80x94CH2COOR10, wherein R10 represents a hydrogen atom, a linear or branched, substituted or unsubstituted alkyl group having 1-20 carbon atoms, or a substituted or unsubstituted monovalent alicyclic hydrocarbon group having 3-20 carbon atoms.
The above polycyclic compound is preferably selected from the group consisting of the compounds of the following formulas (4) and (5): 
wherein R11, R12, and R13 individually represent a hydrogen atom or a hydroxyl group, provided that at least one of the groups R11, R12, and R13 is a hydroxyl group.
The content of the above polycyclic compound is preferably 1-20 parts by weight per 100 parts by weight of the resin (A).
In sill another embodiment of the present invention, the radiation-sensitive resin composition, the content of propylene glycol monomethyl ether acetate, xcex3-butyrolactone, and cyclohexanone is respectively in the range of 10-89 wt %, 1-40 wt %, and 10-89 wt %.
The resin (A) in the radiation-sensitive resin composition of the present invention preferably has a polystyrene-reduced weight average molecular weight determined by gel permeation chromatography of 3,000-30,000.
The radiation-sensitive resin composition of the present invention is preferably dissolved in the solvent to make the solid component concentration in the range of 5 to 50 wt %.
In a further preferred embodiment of the radiation-sensitive resin composition, the content of the acid generator (B) is preferably 0.1-20 parts by weight per 100 parts by weight of the resin (A).
Other objects, features and advantages of the invention will hereinafter become more readily apparent from the following description.